Signaling system



Feb. 28, 1939. PULUS 2,148,578

SIGNALING SYSTEM Filed July 11, 1935 6/ GAS FILLED 5 IIIIII L lNVENTORBy G. A. PULL/5 A T TOR/V5 V Patented Feb. 28, 1939 PATENT OFFICESIGNALING SYSTEM A. as

New York, Telephone laboratories,

N. Y., assignor to Incorporated,

New York, N. Y., a corporation of New York Application July 11, 1935,Serial No. 30,843 4 Claims. (Cl. 250-27) This invention relates totransmission systems and more particularly to improvements in signalingarrangements associated with such systems.

The selective signaling arrangements of the invention are useful in tolltelephone systems employing signaling currents within the voicefrequency range. In one specific system of this character a signalingcurrent of base frequency of 1000 cycles is transmitted which may beinterrupted at difierent low frequency rates such as 15, 25, or 35cycles. Selective signaling apparatus is used in various capacities eachapparatus being tuned to operate at a particular low frequency rate. Thebase frequency and the fre quency of the interruptions may be greatlyvaried as shown in the art. Another specific system of this characterembodies a multi-channel voice frequency signaling arrangement.

In some voice frequency selective signaling systems it has been thepractice to utilize series resonant circuits tuned to various lowfrequencies for actuating signals of distinguishing characteristics.These circuits comprise cumbersome and expensive apparatus such as largeand very accurately made retardation coils in series with condensers ofvarious capacities. Other voice frequency selective signaling systemsutilize sensitive polarized relays which are actuated by the output of atwo-stage receiving amplifier detector. The polarized relay, through itscontacts, causes a condenser to be alternately charged and dischargedthrough a local direct current relay and an inductance which tunes thecircuit to the low frequency transmitter. The aforementioned inductanceused in this system is again a very cumbersome and expensive piece ofapparatus.

It is therefore the object of this invention to provide a selectivesignaling circuit which may be accurately tuned to voice frequencycurrents or to low frequency interruptions of voice frequency currents,using apparatus which may be economically manufactured and convenientlymounted in a small space.

In the arrangement of the invention a small and economically madeinstrument known as a transducer is utilized in combination with agasfilled thermionic tube for operating the selective signalingapparatus according to the frequency or combination of frequenciestransmitted. The transducer of each signaling circuit may be easily andvery accurately tuned to the frequency designated for the operation of aparticular signaling instrument. The transducer comprises a driving coiland a pick-up coil which are independent of each other and independentof mutual coupling.

line and receives the signaling rent flow in the relay is maintaineduntil a circuit change takes 30 A reed is mounted between the coils andis arranged to be vibrated by the driving coil in a manner to change thecross-sectional area of the reluctance gap of the pick-up coil inresonance with the frequency of the current transmitted through thedriving coil. From the foregoing it is apparent that the driving coil isconnected through an output transformer to the toll current transmittedover this line. The pick-up coil is con- 1. nected in a direct currentcircuit with the grid and anode of a gas-filled thermionic tube. The

- change in the cross-sectional area of the reluctance gap of thepick-up coil actuates a current flow in the grid circuit of thethermionic tube to II start a gaseous discharge path in said tube andconsequently create a current flow in the plate circuit for operating asignaling relay. The curplate circuit for operating the place to quenchthe discharge started by the operation of the transducer.

The invention may be more fully understood from the followingdescription, together with the accompanying drawing, Figs. 1 and 2, inwhich the invention is illustrated.

Fig. 1 is a circuit diagram embodying apparatus for low frequencysignaling; and

Fig. 2 is a circuit diagram embodying apparatus for signaling in thevoice frequency range. 30

Fig. 1 illustrates a transmission line L over which signaling currentsmay be transmitted. For example, a base frequency of 1000 cycles may beused for signaling purposes. In order to ob tain several distinctivesignals, this base fre- 35 quency may be interrupted at different rates,such as 15, 25 and 35 cycles. A signal receiving circuit bridged acrossline L at a particular station and is tuned to the signaling frequenciestransmitted over line L to said station. The 40 1000-cycle basefrequency signal current inter rupted at the rated 15, 25 or 35 cyclesreceived from line L is stepped up by the input transformer 2 andapplied to the grid 8 of the thermionic amplifier tube 6. The amplifiedcurrent is then applied to the output transformer it over the platecircuit of tube 6. The output current is rectified by means of the fullwave rectifier l5 which may be a copper oxide rectifier as shown. Therectified current is transmitted in series through driving coils 23, 24,25, 26, 21, and 28 of the transducers, 20, 2|, and 22. Let it be assumedthat the transducer 20 is tuned to respond to a frequency rate of 15cycles, that transducer 2| is tuned to respond to a frequency rate of 25cycles, and that transducer 22 is tuned to respond to a frequency rateof 35 cycles. The transmission of one of the above frequencies operatesa signaling circuit A, B, or 0 having the transducer which is tuned tothe particular low frequency interruption transmitted. If the frequencyof the interruptions is at the rate of 15 cycles, it may be assumed thatthe transducer 20 responds for operating the signaling circuit A.

Each transducer comprises a pair of driving coils, such as 23 and 24, apair of pick-up coils, such as 30 and 3|, and a reed, such as 36, tunedto operate at a particular frequency. The reed terminates in a bar piecewhich extends between the coil pole-pieces. A signal of the properfrequency transmitted through the driving coils causes the reed and barto vibrate transversely in the direction of the arrows in resonance withthe frequency transmitted. The driving coils and the pick-up coils areindependent of mutual coupling. Thus, an interrupted current transmittedthrough the driving coils can only generate a voltage in the pick-upcoils by vibrating the reed to change the cross-sectional area of thereluctance gap. This creates an alternating current in the pick-up coilsof a voltage to start an are between the control electrode 42 andcathode 4| of the gas-filled thermionic tube 40. A current flow is thuscreated in the anode-cathode circuit which may be traced from anode 43through the winding of relay 46 to the positive pole of battery 48. Therelay 46 is wound and adjusted to operate on the anode-cathode currentilow for closing its contact to establish a circuit for signal lamp 41.This circuit may be traced from ground through the relay contact andfilament of lamp 41 to battery 49.

With a gas-filled tube such as 40, once the arc has started, it willcontinue without further application of an input signal if a suitableanodecathode voltage is maintained without superposed alternatingcurrent to quench the are. In the arrangement described a condenser 45and resistance 44 are serially connected between the anode 43 andcathode 4|. With no input potential on the tube due to the linethebattery in the input circuit maintains a sufliciently negative potentialon the control electrode 42 to prevent an anode-cathode discharge due tothe battery 48. Further, condenser 45, when no discharge is takingplace, is charged to the potential of battery 48. When the transducerresponds to line voltage and the control electrode 42 swings positive, adischarge occurs between the anode and oath ode, due to battery 48, andcurrent starts to flow in the output circuit including relay 46 whichthereupon operates. Due to the lowered resistance of the anode-cathodegap at this moment condenser 45 also starts to discharge in a circuitincluding resistance 44 and the anodecathode gap. By properly choosingthe value of the condenser 45 and resistance 44 with respect to theimpedance of relay 46, the condenser 45 will rapidly discharge to such alow potential that the arc discharge between the anode and cathode willbe extinguished.

As soon as the charge on condenser 45 drops below its initial valuecurrent will start to flow from battery 48, through relay 46 to rechargethe condenser to the battery voltage, but owing to the values chosen forthe elements of the circuit, condenser 45 will discharge much morerapidly than it can charge until the current through the tube drops tozero, which occurs as soon as the voltage across condenser 45 is too lowto maintain the are between the anode and cathode.- The tube outputcurrent is thus interrupted, but current will continue to flow frombattery 48 through the winding of relay 46 and into condenser 45 untilit is recharged to the point at which the anode-cathode voltage of tube40 reaches the value sufflcient to cause the tube to again break down.When this occurs a comparatively large current will again flow fromcondenser 45 through the anode-cathode path of tube 40 again dischargingthe condenser to a value which is insufficient to maintain thedischarge. Thus, the tube will alternately flre and be extinguished,when condenser 45 is charged and discharged, as long as the controlelectrode 42 of tube 40 is at a voltage such that the battery voltage 48is sufficient to cause the tube to fire. There will, however, be acontinuous flow of current from the battery 48 through the relay 46 bothwhen the condenser 45 is charging and when it is discharging so thatrelay 46 will hold operated as long as the control electrode 42 of tube46 is more positive than the critical potential required for an arc tostrike between the anode and cathode. The voltage of the biasing batteryfor the control electrode 42 must be more negative than this criticalvalue so that, upon the removal of the input voltage or during thenegative half cycles thereof, no discharge can take place.

' In order that relay 46 may remain operated throughout the negativehalf cycles of input potential, it is merely necessary that thecondenser 45 shall not be fully charged through the impedance of relay46, during this interval, but on the removal of the input voltage, asthe tube does not again become conducting, the condenser will soonbecome fully charged and current in the winding of relay 46 will ceaseto flow and the relay will release. the foregoing is that the frequencyof the chargedischarge cycle 01 condenser 45 must be low in comparisonto the input frequency delivered by the pick-up windings of thetransducer. This circuit may be slightly altered in any well-knownmanner to obtain a locking input signal which may be extinguished at thewill of the operator.

The circuits B and C operate in the selective signaling circuit in thesame manner as circuit A with the exception of the transducers which, asherein stated, are adjusted for operation on different inputfrequencies. The arrangement is not limited to three signaling branchessince the number may be increased as required.

In certain instances the relays such as 46 and lamp such as 41 may beomitted and the light caused by the arc in the gas-filled thermionictube used as the signaling means.

The circuit arrangement of Fig. 2 comprises a multi-channel voicefrequency signaling system. Signaling currents within the voicefrequency range may be transmitted over line L for the selectiveoperation of the signals of this circuit. The signaling currenttransmitted may be of a single frequency or a combination offrequencies. The preferred system uses a combination of voicefrequencies within the range of'500 cycles to 900 cycles. Thefrequencies may be selected as 500 cycles, 600 cycles, 750 cycles, and900 cycles, and the transducers 68, 69, i0 and H tuned accordingly. Thecombinations of frequencies which may be simultaneously transmitted overline L may be as follows: 500, 750, and 900; or 500, 600, and 700; or500, 600, and 900. The circuit illustrated in Fig. 2 is arranged forselective opera- Another way of stating arcane The foregoing voiced'requency currents are impressed upon the input coil 82 connected incir-.

cuit with the vacuum tube amplifier which impresses the amplifiedcurrent upon the output coil 81. Let it be assumed that the transducer88 is tuned to operate at the rate of 500 cycles, transducer 69 at therate of 600 cycles, transducer "at the rate of 750 cycles, andtransducer H at the rate of 900 cycles. The transmission of theforegoing first combination causes the impression of 500, 750, and 900cycles currents upon the driving coils of the transducers and cause thereeds of transducers 68, I8, and H to vibrate for changing thecross-sectional area of the reluctance gap of these coils in resonancewith these frequencies. A current is thus created in the pick-up coilsof transducers 68, I8, and ll of a voltage to start an are between theanodes and cathodes of the gas-filled thermionic tubes 12, 88 and 81 ofsignaling branches D, F, and G. A current is thus created in the platecircuits of the signaling branches D, F, and G for energizing relays 88,82, and 83 as described for the signaling relays of Fig. 1. Theoperation of relay 88 establishes a circuit for the operation of relay84 which may be traced from ground through the front contact of relay88, rear contact of relay 8|, winding of relay 84, to battery. Theoperation of relay 84 disconnects lamps F and G from'the signalingsystem and establishes a circuit for lamp E. The circuit for lightinglamp E may be traced from ground through the front contact of relay 88,back contact of relay 8i, front contact 98 of relay 84, front contact ofrelay 82, front contact 9| of relay 84, front contact of relay 83, frontcontact 92 of relay 84, lamp E, to battery. A second combination offrequencies, such as 500, 600, and 700 cycles causes the operation oftransducers 68, 89, and 18 which breaks down the gas-filled thermionictubes I2, 85 and 88 of circuits D, E, and F for operating relays 88, 8i,and 82. The operation of these three relays establishes a circuit forlamp F which may be traced from ground through the front contact ofrelay 88, front contact of relay 8|, front contact of relay 82, backcontact 9| of relay 88, lamp F, to battery. The third combinationcomprising the transmission of 500, 600, and 900 cycle currents causesthe operation of transducers 68, 69, and H. An arc is thus started inthe gas-filled thermionic tubes of signaling branches D, E, and G forthe operation of relays 88, 8|, and 83. A circuit is thus establishedfor the illumination of lamp G which may be traced from ground throughthe front contact of relay 88, front contact of relay 8|, front contactof relay 83, back contact 82 of relay 8|, lamp G, to battery.

What is claimed is:

1. In a frequency selecting receiver, a transducer comprising a magneticstructure, driving and pick-up coils wound thereon and a tuned reedadapted to be vibrated by current of the desired frequency applied tothe driving coil and to general alternating current of a like frequencyin the pick-up coil, an electromagnetic signal controlling device, and agas-filled discharge device having an anode, a cathode, and a controlelectrode, an input circuit therefor including said pick-up coil, saidcathode, and said control electrode, and an output circuit thereforserially including a source of direct current, said signal controllingdevice, and said anode and cathode,

and a condenser and a current limiting impedance seriaiiv connectedbetween said anode and cathode in parallel with said direct currentsource and signal controlling device, said output circuit elementshaving such values with respect to each other that when the inputpotential generated in said pick-up coil is of such a value as to causean arc discharge to occur between said anode and cathode said signalcontrol device will operate and remain operated until the value of saidinput potential has been less than that required to initiate said aredischarge for a period longer than the duration of onehalf cycle of saidinput frequency.

2. In a frequency selecting receiver, a transducer comprising a magneticstructure. driving and pick-up coils wound thereon, and a tuned reedadapted to be vibrated by current of the desired frequency applied tothe driving coil and to generate alternating current of a like frequencyin the pick-up coil, an electromagnetic signal controlling device, and agas-filled discharge device having an anode, a cathode and a controlelectrode, an input circuit therefor including said pick-up coil, saidcathode, and said control electrode, and an output circuit thereforserially including a source of direct current, said signal controllingdevice, and said anode and said cathode, and a condenser and a currentlimiting impedance serially connected between said anode and cathode inparallel with said direct current source and signal controlling device,said output circuit elements having such values with respect to eachother that the time constant of said condenser and current limitingimpedance, when a discharge is taking place between said anode andcathode, is substantially less than the time constant of said signalcontrolling device under the same condition.

3. In a frequency selecting receiver, a transducer comprising a magneticstructure, driving and pick-up coils wound thereon; and a tuned reedadapted to be vibrated by current of the desired frequency applied tothe driving coil and to generate alternating current of a like frequencyin the pick-up coil, an electromagnetic signal controlling device, and agas-filled discharge device having an anode, a cathode and a controlelectrode, an input circuit therefor including said pick-up coil, saidcathode and said control electrode, and an output circuit thereforserially including a source of direct current, said signal controllingdevice, and said anode and cathode, and a condenser and a currentlimiting impedance serially connected between said anode and cathode inparallel with said direct current source and signal controlling device,said output circuit elements having such values with respect to eachother that said condenser will alternately discharge through said aredischarge path and charge from said direct current source through saidsignal controlling device to alternately extinguish and strike said arcdischarge until said input potential has been reduced below the valuerequired to initiate said are discharge.

4. In a frequency selecting receiver, a transducer comprising a magneticstructure, driving and pick-up coils wound thereon, and a tuned reedadapted to be vibrated by current of the desired frequency applied tothe driving coil and to generate alternating current of a likefrequencyin the pick-up coil, an electromagnetic signal controllingdevice, and a gas-filled discharge device havlng an anode, a cathode anda control electrode, an input circuit therefor including said pick-upcoil, said cathode and said control-electrode, and an output circuittherefor serially including a source of direct current, said signalcontrolling device, and said anode and cathode, and a condenser and acurrent limiting impedance serially connected between said anode andcathode in parallel with said direct v current source and signalcontrolling device, said output circuit elements having such values withrespect to each other that said condenser will discharge through saidimpedance and the anode-cathode path more rapidly than it can chargefrom said direct current source through said signal control device.

GEORGE A. PUILIS.

